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H S An

Publications and source records attributed to H S An.

At least 55 records · Page 3Linked to original sources
PubMed1998

Saline injection technique to confirm pedicle screw path: a cadaveric study.

Pedicle screws are frequently misdirected during placement, which may lead to complications such as pedicle fracture, inadequate biomechanical strength, and neurologic deficit. Roentgenographic confirmation and manual probing are important but are not 100% accurate. We have developed a simple saline injection technique to assist in confirming the correct path of the pedicle screw prior to its insertion. In this study, five fresh frozen cadaveric spines were dissected from T-12 to L-5, and a total of 60 data points were recorded. Saline injection tests confirmed 31 of 32 (97%) drill paths that were in the pedicles. Two specimens were used to intentionally misdirect the pedicle drill path to determine the rate of false-negative results. Pedicle drilling was misdirected medially, laterally, superiorly, and and inferiorly (six of each). There were a total of 24 intentional and four unintentional, radiographically confirmed missed drillings of the pedicle. Of the 28 misdirected pedicle paths, the saline injection test correctly diagnosed the problem in 23 (82%) cases. Seven misdirected drillings were falsely negative by the injection test (five superior and two inferior directions). This study shows that a simple saline injection test can be a useful adjunct in confirming a correct pedicle path in 97% of the cases. If an incorrect path has been created, false-negative tests are possible in 18% of the cases.

Bone Screws↗
PubMed1998

Contrast media of high and low molecular weights in the detection of recurrent herniated disks.

PURPOSE: Our goal was to compare contrast enhancement of recurrent herniated disk fragments and scar after intravenous injection of a new high-molecular-weight contrast medium, Gadomer 17 (gadomer), with that after injection of a low-molecular-weight contrast medium, (gadopentetate dimeglumine). METHODS: Recurrent herniated disks were modeled in dogs by placing a fragment of intervertebral disk cartilage in the epidural space at laminectomy. MR imaging was performed with one of the contrast media at 20 and 50 days and with the other medium at 22 and 52 days. The changes in signal intensity from baseline in the disk fragment and in the adjacent scar tissue was measured at 2, 22, and 45 minutes. Differences were tested for significance with a student t-test. RESULTS: At 50 days after surgery, signal intensity in the intervertebral disk fragment increased by an average of 0.52 at 2 minutes after injection of gadomer and by an average of 0.90 after injection of gadopentetate. For scar, the increases in signal intensity were 1.41 (gadomer) and 1.62 (gadopentetate). At 22 and 45 minutes after injection, the signal intensity change in the disk fragment continued to be significantly greater after gadopentetate than after gadomer injection. In comparison with the changes at 50 days, both scar and disk fragment tended to show greater signal intensity changes at 20 days. Signal intensity changes in the disk fragments were significantly less after gadomer than after gadopentetate. Signal intensity changes in scar were slightly less with gadomer than with gadopentetate. CONCLUSION: Greater contrast is achieved between scar and recurrent herniated disk with a higher-molecular-weight contrast medium than with one of lower molecular weight. The difference between the high- and low-molecular-weight contrast media increases with maturation of the scar tissue.

Animals↗
PubMed1998

Oblique MRI as a useful adjunct in evaluation of cervical foraminal impingement.

Magnetic resonance (MR) imaging is considered the gold standard for soft-tissue disease. The traditional MR imaging series uses axial and sagittal views. The purpose of this study was to demonstrate that oblique MR imaging provides valuable information about the cervical foramen not available from the conventional MR imaging technique. Ten asymptomatic individuals volunteered for MR imaging. Measurements were taken of height, width, and area for the nerves and foramen at the entrance and mid zones. Nerves were graded as normal, contacted, or deformed. Normal foraminal morphology in asymptomatic individuals and characteristics that compromise the space available for the nerve root were identified. Nerves with minimal or no contact had significantly greater foraminal widths than nerves with significant contact. Although there was a correlation between nerve contact and foraminal width, regression analysis did not demonstrate a correlation between disc height and foraminal size.

Adult↗
PubMed1997

A noninvasive, three-dimensional spinal motion analysis method.

STUDY DESIGN: A three-dimensional, noninvasive motion analysis method was developed by monitoring the orientation of the principal axes of each vertebra. OBJECTIVES: To develop a method of performing three-dimensional, noninvasive motion analysis of the spine using computed tomography data. SUMMARY OF BACKGROUND DATA: The concept of using principal axes of the moment of inertia tensor to measure the orientation and position of a rigid body has been applied to the wrist and subtalar joints, but has not yet been applied to the spine. METHODS: Scans were taken of two isolated vertebrae in various known positions. Centroids, area, moments, and product of inertia of each scan were determined using a commercial program. Custom software combined data using the parallel axis theorem to give three-dimensional data for each vertebra. Changes in the centroid and principal axes were used to calculate translation and rotation, respectively. RESULTS: The system accuracy was within 1.0 degree in rotation and 1.0 mm in translation. Some errors occurred in minor motions when a smaller number of scans were used. System resolution was 0.43 mm. CONCLUSIONS: A system has been developed capable of calculating three-dimensional spinal motion based on measurements of a series of computed tomography images. The system has an accuracy similar to that of current motion analysis methods, but future studies will be necessary to apply this system in vivo.

Cadaver↗
PubMed1997

Biomechanical evaluation of anterior and posterior fixations in an unstable calf spine model.

STUDY DESIGN: Fresh calf lumbar spines were used to perform flexibility tests in multiple loading directions to compare the stabilizing effects of anterior and posterior rigid instrumentations. OBJECTIVE: To compare the biomechanical flexibility of anterior and posterior instrumentation constructs using an unstable calf spine model. SUMMARY OF BACKGROUND DATA: Unstable burst fractures of the thoracolumbar spine can be managed anteriorly or posteriorly. Controversy persists, however, on the merit of anterior fixation versus that of posterior fixation in terms of how much stability can be achieved. METHODS: Fifteen fresh calf spines (L2-L5) were loaded with pure unconstrained moments in flexion, extension, axial rotation, and lateral bending directions. After removal of L3-L4 disc and endplates to create an 1.5-cm anterior and middle column defect, testing was performed on five specimens after anterior Kaneda rod fixation, anterior University Plate fixation, or posterior ISOLA pedicle screw fixation (AcroMed, Cleveland, OH). Testing was repeated after inserting a polymethylmethacrylate block to stimulate an interbody anterior graft with instrumentation. RESULTS: All fixation devices provided a significant stabilizing effect in flexion and lateral bending. In extension, all constructs except ISOLA (AcroMed) without graft were stiffer than the intact specimen. In axial rotation with no graft, only the Kaneda device significantly reduced the flexibility from that of the intact specimen. The interbody graft provided additional rigidity to the ISOLA (AcroMed) instrumentation construct in flexion and extension and to the Kaneda construct in lateral bending. There was no significant effect of grafting in axial rotation. CONCLUSIONS: A short, transpedicular instrumentation, such as ISOLA (AcroMed), provided less rigid fixation in flexion and extension without the anterior structural graft. The Kaneda rod and University plate with grafting provided a significant stabilizing effect in all directions compared with the intact specimen. When no graft was inserted, the Kaneda device was more effective in preventing axial rotation than the other devices. In lateral bending, the University plate provided more rigid fixation than the Kaneda device without grafting.

Animals↗
PubMed1997

Posterior cervical fixation for fracture and degenerative disc disease.

There are numerous newer techniques that have been developed for the internal fixation of the cervical spine in recent years. Wiring techniques are still appropriate for posterior stabilization of the cervical spine. The halo vest is still widely used for the conservative management of cervical fractures and for postoperative external immobilization. The authors stress that the surgical indications for more modern rigid implants should be adhered to strictly. These implants also should be selected by weighing their advantages versus potential risks. In the upper cervical spine, the surgeon may choose traditional wiring methods and newer C1-C2 screw fixation, occipitocervical plate fixation. For the lower cervical spine, triple wiring technique or lateral mass plating may be used. The surgeon must choose an appropriate device based on the mechanism of injury, pathoanatomy of the lesion, and familiarity with the device, keeping in mind that the goals of internal fixation are stabilization, reduction and maintenance of alignment, early rehabilitation and perhaps enhancement of fusion rates, and avoidance of use of an external halo vest.

Adolescent↗
PubMed1997

Lumbar spine surgery in the obese patient.

A prospective study was performed in obese and nonobese patients undergoing lumbar spine surgery to report perioperative data and surgical outcomes. One hundred fifty-nine consecutive patients who underwent lumbar spine surgery by a single surgeon entered the study. Among 159 consecutive patients, 55 met the criteria for obesity (> 20% ideal body weight). The average weight was 226 lb in the obese group. There were 28 men and 27 women with ages ranging from 25 to 81 years, with a mean of 47.9 years. The diagnoses and procedures included 31% herniated nucleus pulposus with laminotomy and discectomy, 14% spinal stenosis with laminectomy, and 55% lumbar fusion procedures for other disorders. Twenty-nine percent had previous lumbar surgery that had failed. Results indicated that there were no significant differences between the obese and control groups in terms of duration of surgery (3.8 versus 3.2 h), blood loss (723 versus 605 ml), and duration of hospital stay (5.6 versus 5.8 days). The clinical results were 24% excellent, 40% good, 27% fair, and 9% poor in the obese group; and 27% excellent, 37% good, 19% fair, and 17% poor in the control group. This study found no significant differences between obese and control patients relative to blood loss, operative time, hospital stay, rate of complications, and functional outcome in lumbar spine surgery. Patient selection continues to be the most important factor in terms of operative success. We believe that lumbar spine surgery, including fusion, should not be withheld from obese patients who present with proper indications for surgery and fail an appropriate course of conservative treatment.

Adult↗
PubMed1996

Anatomic changes of the spinal canal and intervertebral foramen associated with flexion-extension movement.

STUDY DESIGN: A cadaveric study was done to analyze the dimensional changes in the spinal canal and intervertebral foramen of the lumber spine with flexion and extension movements. OBJECTIVES: To investigate the relationship between flexion and extension movements and morphologic changes in the spinal canal and the intervertebral foramen. SUMMARY OF BACKGROUND DATA: Previous studies have reported that the dimensions of the spinal canal and the intervertebral foramen may change significantly with motion. The purpose of this study was to assess the quantitative changes in the spinal canal and the intervertebral foramen with segmental flexion-extension movements. METHODS: Nineteen fresh cadaveric spines yielding 25 motion segments were used. The lumbar motion segments were frozen and then imaged in axial and sagittal projections by a computed tomography scanner. They were thawed then, and the motion segments were loaded to 5.7 Nm in flexion (13 motion segments) and in extension (12 motion segments) specimens. While in flexion or extension, the specimens again were frozen and imaged by computed tomography scan. The frozen specimens than were sliced using a cryomicrotome in the sagittal plane to study the dimensions of the intervertebral foramen. Eighteen other fresh cadaveric spines were sliced sagittally for study in the neutral position. RESULTS: The axial computed tomography scans showed that extension significantly decreased the canal area, midsagittal diameter, and subarticular sagittal diameter, whereas flexion had the opposite effects. The sagittal computed tomography scans showed that extension decreased all the foraminal dimensions significantly, whereas flexion increased all the foraminal dimensions significantly. The translational changes were associated with the bulging of the disc and the presence of traction spurs. The cryomicrotome sections showed the cross-sectional area of the foramen to be 12% greater for the flexion group and 15% smaller for the extension group than the cross-sectional area of the neutral group. Nerve root compression in the foramen was found to be 21.0% in neutral, 15.4% in flexion, and 33.3% in extension groups. CONCLUSIONS: The study supports the concept of dynamic spinal stenosis. In addition to static anatomic changes, careful dynamic studies may be required to evaluate better the central canal and the foramen.

Adult↗
PubMed1996

The ideal amount of lumbar foraminal distraction for pedicle screw instrumentation.

STUDY DESIGN: A cadaveric study was performed to analyze the changes of foraminal dimensions of the lumbar spine and also to estimate the amount of foraminal distraction, achieved with pedicle screw instrumentation, that will create the greatest improvement in foraminal dimensions. OBJECTIVES: To establish the ideal amount of lumbar foraminal distraction using pedicle screw instrumentation and to investigate the changes of adjacent segments and lumbar lordosis with distraction maneuvers. SUMMARY OF BACKGROUND DATA: In patients undergoing fusions and instrumentation for foraminal stenosis, distraction of the lumbar spine may improve the dimensions of the intervertebral foramen. Results of previous studies have shown that anterior interbody distraction of the lumbar spine significantly increased the space in the lumbar foramen. No previous study has assessed the ideal amount of distraction, changes in the adjacent segments, or the effect on lumbar lordosis using posterior pedicle screw instrumentation. METHODS: Six fresh frozen human cadaveric spines from 15 to the sacrum were used. The ISOLA instrumentation system (Acromed Inc., Cleveland, OH) was applied using pedicle screws at L4, L5, and S1, L4-L5 and L5-S1 rods were contoured to the same degree of lumbar lordosis as in the specimen. The spine was potted in the upright position with the sacrum secured in the mold, and an axial load of 40 pounds was applied to the specimen. Radiographs were used to measure the posterior disc height, foraminal height, foraminal area, and lumbar lordosis. Two mm, 4 mm, 6 mm, 8 mm, and 10 mm of single level distraction were added to L4-L5 and L5-S1. The dimensions of the specimen were digitized and calculated after each distraction. RESULTS: The posterior disc height, foraminal height and foraminal area increased with distraction. The greatest incremental change in the foraminal area was noted at 6 mm of distraction. The L4-L5 foraminal area increased 22.6% at 6 mm of L4-L5 distraction, and the L5-S1 foraminal area increased 39.2% at 6 mm of L5-S1 distraction. With distraction above 6 mm, the foraminal change plateaued. The greatest decrease in lumbar lordosis was only 4.6 degrees and occurred at 10 mm of distraction. There was no significant effect of distraction on the foramina of adjacent levels. CONCLUSION: Posterior distraction using pedicle screws increased foraminal dimensions. The ideal amount of distraction on the rod, or the minimal amount of distraction necessary for improving foraminal dimensions, may be 6 mm using pedicle screw instrumentation.

Aged↗
PubMed1996

Biomechanics of transfixation in pedicle screw instrumentation.

STUDY DESIGN: The biomechanical role of transfixation in pedicle screw instrumentation was investigated using flexibility tests and finite element analyses. OBJECTIVE: To assess the stabilizing effect of use and position of transfixators. SUMMARY OF BACKGROUND DATA: Transfixation is common in pedicle screw instrumentation, however, its biomechanical role and optimal position are not completely understood. METHODS: Specimens underwent nondestructive flexibility tests using a three-dimensional motion analysis system. Tests compared the intact spine with instrumentation with and without transfixators Rotational angles of the superior vertebra, resulting from the maximum moment of 6.4 Nm, were compared. Three-dimensional finite element models investigated transfixator position. Rotations of the superior vertebra were compared for cases with and without transfixators to determine the position providing the greatest stability. RESULTS: Biomechanical test showed that only axial rotational stability significantly improved with transfixators compared with instrumentation alone. Pimte element models predicted improvement in lateral bending and axial rotation with transfixators compared with the case with no transfixator. With one transfixator, the greatest improvement in axial rotation stability occurred with the transfixator at the proximal 1/4 position of the rods. When two transfixators were used, the optimal locations were with one transfixator in the middle and the second at the proximal 1/8 position. CONCLUSIONS: Transfixators improved the stabilizing effects of pedicle screw instrumentation. The greatest axial rotation stability was obtained with two transfixators; one in the middle and the other at the proximal 1/8 position of the longitudinal rods.

Animals↗
PubMed1996

Isolation of 88F actin mutants of Drosophila melanogaster and possible alterations in the mutant actin structures.

The 88F actin (act88F) gene of Drosophila, melanogaster encodes an actin isoform that is expressed exclusively in the indirect flight muscle. In order to isolate a large number of act88F mutants, an efficient screening method was used to obtain dominant flightless mutants. Genetic analyses revealed that 25 mutations were located near or at the act88F locus. From each mutant strain, the DNA fragments including the coding region of the act88F gene were asymmetrically amplified by the polymerase chain reaction method, and the amplified fragments were directly sequenced. Eighteen of them were found to have point mutations within their coding regions. Of these, 13 were novel alleles of this gene. We have characterised these mutations in detail. First, their flight abilities were tested after introducing two normal alleles of this gene. Second, two-dimensional gel electrophoresis was used to examine actin isoforms and whole thorax proteins. Third, morphological anomalies of indirect flight muscle fibres and myofibrils were examined with an optical microscope. On the basis of these phenotypes and the known atomic structure of actin, possible alterations in the structure of actin brought about by these mutations are discussed.

Actins↗
PubMed1996

The quantitative anatomy of the cervical nerve root groove and the intervertebral foramen.

STUDY DESIGN: The present study evaluated the cervical nerve groove and intervertebral foramen using dried vertebrae and cadaveric cervical spine. OBJECTIVES: To measure the cervical nerve groove in eight linear and one angular dimensions and the intervertebral foramen in two linear diameters. SUMMARY OF BACKGROUND DATA: Several anatomic studies of the cervical spine exist, but very little quantitative data have been reported on the cervical nerve groove. METHODS: Dried cervical vertebrae, C3-C7, from 41 complete vertebral sets (205 vertebrae) and 14 cadaveric cervical spine were obtained for the present study. Anatomic evaluation focused on the cervical nerve groove for dry specimens and intervertebral foramen for cadaveric specimens. Ten linear and one angular measurements were made bilaterally. The mean, range, and standard deviation were calculated for all of the specimens and for male and female specimens separately. RESULTS: Differences in dimensions of male and female specimens were not found to be statistically significant. The average lengths of the medial zone and distances from the midline of the vertebral body to the anterior border of the medial zone for male and female specimens consistently increased from C3 to C7. The width of the medial zone was larger in C3 than that of C4, C5, and C6 in male and female specimens. The minimum width for all levels ranged 1-2 mm. The medial zone depths gradually increased from C3 (3.2 mm for male and 2.3 mm for female specimens) to C7 (4.9 mm for male and 4.4 mm for female specimens). The smallest anteroposterior distances from the posterior midpoint of the lateral mass to the posterior border of the nerve groove were found in C7 (6.7 mm for male and 6.1 mm for female specimens). The general trend of the foraminal height and width increased from the cephalad to caudal except at C2-C3. CONCLUSIONS: These data may enhance understanding of the important bony elements associated with the cervical spinal nerves and roots as they pass through the cervical nerve groove and the intervertebral foramen.

Adult↗
PubMed1996

Morphometric analysis of the lumbosacral nerve roots and dorsal root ganglia by magnetic resonance imaging.

STUDY DESIGN: Lumbosacral nerve roots and dorsal root ganglia in relation to surrounding bony structures in normal subjects were investigated using magnetic resonance imaging. OBJECTIVES: This study determined the normal anatomic parameters of the lumbosacral nerve root and dorsal root ganglion, to which degenerative or pathologic changes may be compared. SUMMARY OF BACKGROUND DATA: In the previous literature, most authors have used various modalities in either cadavers or symptomatic patients to study the anatomic details of the lumbar nerve roots and dorsal root ganglia. The data in the literature are conflicting, mainly because of individual variations and different degrees of degenerative change in the spine. METHODS: Twenty male volunteers who had no back pain or radiculopathy underwent magnetic resonance imaging. Ages ranged from 22 to 38 years, with a mean of 30.4 years. T1-weighted coronal magnetic resonance images were taken from L1 to S1. Two hundred thirty-three nerve roots were examined, including 36 L1, 40 L2, 40 L3, 39 L4, 40 L5, and 38 S1. nerve roots Measurements were determined using a computer digitizer. RESULTS: The nerve root origin was at a more cephalad level for the caudad nerve roots, particularly the S1. The take-off angels acutely changed at L1 and S1. The length of the nerve roots increased progressively to a maximum at L5, and decreased at S1. The center of the dorsal root ganglion was positioned more cephalad at S1. The average dimension of the dorsal root ganglion gradually increased from L1 to S1. The most striking difference was in the S1 root, which takes off more cephalad, at a more vertical angle, and has the shortest length of any of the nerve roots. The S1 dorsal root ganglion was also unique in that it was the largest and more frequently located intraspinally. CONCLUSION: The anatomy of the lumbar nerve roots and dorsal root ganglia and their relations to bony structures have been better defined in this study. Because of its more medial location, S1 radiculopathy may involve both the nerve root and dorsal root ganglion as a result of either disc herniation or degenerative L5-S1 facet changes. The relatively larger dorsal root ganglia and the greater dorsal root ganglion/foramen height ratios in the lower lumbar region may explain the higher incidence of L5 or S1 radiculopathy, particularly given the propensity to disc degeneration and intervertebral foraminal narrowing in the lower lumbar region.

Adult↗
PubMed1996

Occult lumbar lateral spinal stenosis in neural foramina subjected to physiologic loading.

PURPOSE: To measure the effect of extension, flexion, lateral bending, and axial rotation loads applied to the spine on the anatomic relationship of the spinal nerves in the neural foramen to the ligamentum flavum and the intervertebral disk, anc to determine the effect of disk degeneration on the response to loading. METHODS: Cadaveric lumbar motion segments were examined with CT and MR imaging, loaded with pure moment forces, frozen in situ, reexamined with CT, and sectioned with a cryomicrotome. The morphology of the intervertebral disks was classified on the basis of the appearance of the cryomicrotome sections. The neural foramina were classified as having no evident stenosis, as being stenotic, as having occult stenosis, or as showing resolved stenosis on the basis of the images and sections before and after loading. The stenotic and nonstenotic foramina were stratified by disk level, intervertebral disk classification, and type of loading applied. The effect of spinal level, disk type, and load type on the prevalence of stenosis was studied. RESULTS: On average, extension, flexion, lateral bending, and axial rotation resulted in the ligamentum flavum or intervertebral disk contacting or compressing the spinal nerve in 18% of the neural foramina. Extension loading produced the most cases of nerve root contact, and lateral bending produced the fewest cases. Each of the loading types resulted also in diminished contact between the spinal nerve and the intervertebral disk or ligamentum flavum in some cases. Disk degeneration significantly increased the prevalence of spinal stenosis. All foramina associated with advanced disk degeneration and half of the foramina associated with disks having radial tears of the annulus fibrosus either developed occult stenosis or were stenotic before loading. CONCLUSIONS: The study supports the concept of dynamic spinal stenosis; that is, intermittent stenosis of the neural foramina. Flexion, extension, lateral bending, and axial rotation significantly changed the anatomic relationships of the ligamentum flavum and intervertebral disk to the spinal nerve roots.

Adult↗
PubMed1996

Cervical root entrapment.

This article reviews the clinical syndromes of neck pain with referred pain, radiculopathy, and myelopathy caused by degenerative disorders of the cervical spine. Cervical spine pathology should be considered as a common cause of symptoms when evaluating with any patient with pain in the upper extremity.

Diagnosis, Differential↗
PubMed1995

Prediction of fatigue screw loosening in anterior spinal fixation using dual energy x-ray absorptiometry.

STUDY DESIGN: A biomechanical study was performed to investigate a relation between the bone mineral density of the vertebral body and the number of loading cycles to induce fatigue loosening of an anterior vertebral screw. OBJECTIVES: The objective of this study was to investigate the potential usefulness of dual energy x-ray absorptiometry of measuring bone mineral density of the vertebral body in predicting the fatigue loosening of th anterior vertebral screw. SUMMARY OF BACKGROUND DATA: Loosening of the vertebral body screw is a well know failure in spinal instrumentation, and more commonly observed than pullout failure. The relation between bone mineral density and pullout strength of the screw has been investigated previously, but no studies are available on the fatigue loosening in anterior spinal fixation. METHODS: Bone mineral density was measured using dual energy x-ray absorptiometry and the screw loosening was produce by a cyclic loading in the cephalad-caudal direction. Screw loosening was defined as 1 mm displacement of the screw relative to bone, and the number of loading cycles to induce the screw loosening was obtained and statistically correlated with bone mineral density. RESULTS: There was a positive correlation between the number of loading cycles to induce screw loosening and bone mineral density (R = 0.8, P < 0.01). The average number of loading cycles to induce screw loosening was significantly less for specimens with bone mineral density < 0.45 g/cm2 compared to those with bone mineral density > or = g/cm2. CONCLUSIONS: These findings suggest that bone mineral density may be a good predictor of anterior vertebral screw loosening. Bone mineral density < 0.45 g/cm2 may be critical value of loosening of the anterior vertebral body screw. However, further biomechanical and clinical studies are required before using threshold value clinically.

Absorptiometry, Photon↗
PubMed1995

Evaluation of porous biphasic calcium phosphate ceramics for anterior cervical interbody fusion in a caprine model.

STUDY DESIGN: This study compared the efficacy of characterized 50/50 hydroxyapatite/beta-tricalcium phosphate ceramics of 30%, 50%, and 70% porosity and autograft to promote interbody spinal fusion at C2-C3 and C5-C6 in 24 goats: 12 at 3 months and 12 at 6 months. OBJECTIVES: Radiographs, histology, dual energy x-ray absorptiometry analysis, and biomechanical testing were used to evaluate the ability of the 30%, 50%, and 70% porous 50/50 hydroxyapatite/beta-tricalcium phosphate ceramics and autograft to promote cervical interbody fusion. SUMMARY OF BACKGROUND DATA: The conundrum in the use of calcium phosphates for interbody fusion is what porosity is most effective to promote ingrowth yet strong enough to resist compressive stresses found in the spine? It is known that the ability for bone ingrowth increases and the compressive strength decreases as porosity of the ceramic is increased. Dense ceramics remain intact but may be surrounded by fibrous tissue. Porous ceramics have good ingrowth but may fracture. METHODS: Radiographs were evaluated for fusion and fracture or collapse of the ceramics or autograft. Dual energy x-ray absorptiometry was used to evaluate the fusion mass. Treated motion segments underwent biomechanical testing to quantify the flexibility of the segment. Undecalcified and decalcified histologic analysis were performed to evaluate the presence or absence of a bony union. RESULTS: Thirty percent, 50%, and 70% porous ceramics had better radiographic fusion scores than the autograft at 3 and 6 months. Incidence of ceramic fracture did not increase with porosity and was equivalent to the collapse of autograft, although ceramics maintained disc height when fracture occurred. No statistically significant differences were found between autograft and the porous ceramics with biomechanical testing and peri-implant bone mineral density values as measured by dual energy x-ray absorptiometry. At 3 months, histologic analysis showed a union rate of 0% for autograft and 30% porous ceramic, 67% for 50% porous ceramic, and 83% for 70% porous ceramic. At 6 months, the union rate was 67% for the 30%, 50%, and 70% porous ceramics and 50% for autograft. CONCLUSIONS: Thirty percent, 50%, and 70% porous ceramics performed equal to or better than autogenous bone after 3 and 6 months. There may be promise for the use of 50/50 hydroxyapatite/beta-tricalcium phosphate in spine surgery as the need to harvest autograft from the iliac crest is obviated, and complications and cost associated with the harvest are avoided.

Animals↗